In multi-carrier systems, data is transmitted on multiple subcarriers and then collected at a receiver for the multi-carrier system. OFDM (orthogonal frequency division multiplexed) signals are used by some multi-carrier systems where transmitted data is modulated on a number of closely spaced orthogonal subcarriers. Further, some multi-carrier systems utilize standard transmission protocols to facilitate the detection and synchronization of received signals. For example, a predefined preamble can be used to with respect to data transmissions to allow a receiver to perform both symbol synchronization and frame synchronization in order to determine a reference point to start demodulation of the transmitted signals. Modern power line communication (PLC) systems, for example, utilize a reference preamble and OFDM signals for multi-carrier communications across power lines between transmitters and receivers.
Symbol synchronization is typically required for the receiver to know the precise instant in time that the data is available on the transmission medium. For symbol synchronization in prior receivers, a time-domain correlation of received signal is typically performed with respect to reference symbols, such as P symbols (SYNCP) within the preamble for the G3-PLC standard for PLC systems. However, in the presence of interfering signals, such as tone interferers in PLC channels, symbol synchronization performance can be significantly degraded. In particular, impulsive noise and narrow band interference can result in poor symbol synchronization performance for PLC receivers. Further, PLC channels often include tone interferers and have significant channel and induced noise levels that exceed what is seen in other communication environments, such as UART (Universal Asynchronous Receive Transmit), USB (Universal Serial Bus) and other serial buses as well as RF (radio frequency) communication systems. As such, PLC channels represent particularly harsh environments for symbol synchronization in PLC receivers.
In addition to symbol synchronization, frame synchronization is typically required for a receiver to demodulate modulated data being received from multi-carrier signals through a communication medium. Some multi-carrier communication systems utilize one or more unique symbols within a reference preamble for frame synchronization, such as the SYNCM symbols within the preamble for the G3-PLC standard for PLC systems. In prior receiver systems, frame synchronization is typically performed using time-domain correlation. However, time-domain correlation does not provide accurate results for frame synchronization where the frame-sync symbol(s) (e.g., SYNCM symbol) is significantly degraded by noise or narrow-band interference within the communication channel. Further, such noise and narrow-band interference is a common characteristic of PLC channels, making frame synchronization difficult or unachievable when the noise degrades the frame-sync symbol(s).